Question

A bone fragment was found from an elk which had died 90 years before. What percent of Pb-210 remains? The half-life if Pb-210 is 22 years.

Answer 1

about 5.9%

Explanation:

We assume that the original amount of Pb-210 present at death decays at the given rate. The fraction (f) remaining is multiplied by 1/2 every 22 years, so can be modeled by ...

f = (1/2)^(t/22) . . . . . where t is in years after death

Then, for t=90, the remaining fraction is ...

f = (1/2)^(90/22) ≈ 0.05868 ≈ 5.9%